Tissue engineering provides promising solutions to problems caused by the growing demand for organ/tissue replacement therapies coupled with a chronically low supply of transplantable organs. In the United States, for example, thousands of people are on the national waiting list for organ transplants. Many will likely perish for lack of suitable organ replacements. To lessen and eventually solve the problem of inadequate supply of organs for transplantation, tissue engineers need to be able to build and grow transplantable organs or organ substitutes in a laboratory, with high precision, on large scale, and in a relatively short amount of time.
A variety of methods and devices for tissue engineering have been attempted and developed with limited success. There has been some success, for example, with production of non-vascularized tissues (e.g., cartilage and tendons). However, assembly of vascularized three-dimensional soft organs has not been accomplished.
One of the more promising tissue engineering technologies that is emerging is organ printing. Organ printing is generally a computer-aided, dispenser-based, three-dimensional tissue-engineering technology aimed at constructing functional organ modules and eventually entire organs layer-by-layer. Organ printing technology, prior to the present invention, has been based on seeding individual cells into biodegradable polymer scaffolds or gels, similar to traditional tissue engineering approaches, but using a dispensing apparatus that employs, for example, a technology analogous to an ink-jet printer or more complex three-dimensional rapid prototype printers (which partially explains the origin of the phrase “organ printing”). Once implanted in the scaffold, the embedded cells are cultured in a bioreactor for several weeks during which time the cell population expands. The resulting tissue may be implanted into a patient where the maturation of the new organ may or may not take place.
Organ printing based on deposition of single cells in a scaffold has many of the same shortcomings as traditional tissue engineering. First, it has not yet achieved production of tissues that require provision of a vascular network, which limits the size and type of the tissue that can be produced. It is also difficult to control the structure of the tissue as it grows from the seeds. Thus, tissue having the desired shape and required stability for a target organ cannot be produced reliably. Further, the individually seeded cells may not survive long enough to sufficiently proliferate. After the cells have been seeded in a scaffold a relatively long incubation period is also required to allow the cells enough time to multiply and form a significant amount of tissue.
Therefore, what is needed is a new and improved technology that enables rapid, reliable, and precise building of target organs. What is further needed is a method, combined with appropriate devices, capable of producing mechanically stable and long-lived three-dimensional organotypic tissue structures.